1. Field of the Invention
The invention relates to embedded inductor devices, and in particular to embedded inductor devices with patterned high permeability magnetic layer to enhance inductance and electrical properties.
2. Description of the Related Art
Both passive and active electronic devices in circuits have been developed towards technique regimes such as high frequency, broad band, and miniaturization, and are applicable to a variety of electronic and communication devices including telecommunication, digital computers, and portable appliances. Embedding of electronic devices into the substrate has become a main developing trend to reduce circuit area. More particularly, embedded passive devices such as embedded inductors have been replacing conventional surface mounted technique (SMT) passive devices.
More fabrication steps and materials, however, are needed to realize the embedding of passive devices into a substrate. Some parasitic effects are generated due to the embedding of inductor devices, reducing electrical performance. For example, when inductor devices are embedded into a substrate, both inductance and quality factor of the inductor device are reduced by the loss of the substrate. Thus, embedded inductor devices with higher inductance are needed to meet requirements of a state of the art electronic circuit. Conventionally, inductance, quality factor and self-resonance frequency (SRF) of an embedded inductor device must be considered as designation of electronic circuit.
U.S. Pat. No. 5,329,020, the entirety of which is hereby incorporated by reference discloses a transformer configured with magnetic material to improve performance. A bulk magnetic material is introduced into an inductor coil of a conventional transformer to increase inductance thereof and improve performance. Conventional transfer using bulk magnetic material with high permeability (high-μr) is very difficult to integrate into integrated passive devices (IPDs) and fabrication processes of circuit board.
U.S. Pat. No. 6,429,763, the entirety of which is hereby incorporated by reference discloses an integrated passive device circuit board with inductor devices on a magnetic substrate. Although configuring inductor devices on a magnetic substrate can improve inductor characteristics, the magnetic substrate causes coupling between the inductor device and other devices, resulting in parasitic effect deteriorating quality factor of the integrated passive device at high frequencies.
In an article entitled “On-Chip Spiral Inductors with Patterned Ground Shields for Si-Based RF IC's,” IEEE 1997 Symposium on VLSI Circuits Digest of Technical Papers, the authors disclose disposal of a patterned ground integrated in planar inductor devices on a silicon substrate. The patterned ground is perpendicular to the winding of the planar inductor devices to improve quality factor thereof. But the improvement of the inductance is limited due to material of the patterned ground.
Furthermore, in an article entitled “Experimental Comparison of Substrate Structures for Inductors and Transformers,” IEEE MELECON 2004, May 12-15, 2004, Dubrovnik, Croatia, the authors disclose a polygonal planar inductor device corresponding to patterned ground. The patterned ground is perpendicular to the winding of the polygonal planar inductor device to improve quality factor thereof. But the improvement of the inductance is limited due to material of the patterned ground.
FIG. 1A is a cross-section of a conventional planar embedded inductor device. FIG. 1B is a planar view of a conventional planar embedded inductor device corresponding to FIG. 1A. Referring to FIG. 1A, a planar embedded inductor device 1 includes a substrate 10 and a conductive coil 20 disposed on the substrate 10. A conductive layer 30 is disposed on the back of the substrate 10, and electrically connects the conductive coil 20 through a via hole 12 or contact plug. The conductive layer 30 typically serves as a ground of the conductive coil 20. Overall disposition of the ground results in inducing currents generating parasitic capacitor between the conductive coil 20 and ground. Thus, the improvement of quality factor is limited thereto.
FIG. 1C is a planar view of another conventional planar embedded inductor device. The conductive layer 30 on the back of the substrate 10 is patterned, and electrically connects the conductive coil 20 through a via hole 12 or contact plug. The patterned conductive layer 30 typically serves as a ground of the conductive coil 20. The patterned conductive layer 30 and the conductive coil 20 are separately disposed on both sides of the substrate 10, and are substantially perpendicular to each other at any crossover, thus improving the quality factor. The inductance of the conventional planar embedded inductor device is, however, limited.
FIG. 2A is schematic view of a conventional planar embedded inductor device. The planar embedded inductor device comprises a substrate 40 and a magnetic layer 42 with high permeability (μr>1) disposed on the substrate 40. Note that the magnetic layer 42 is not patterned. A conductive coil 41 is disposed on the magnetic layer 42 with high permeability (μr>1). The substrate 40 includes polymer substrate or ceramic substrate. The conductive coil 41 electrically connects a conductive layer 46 on the back of the substrate 40 through a via hole 46 or contact plug, thereby generating a loop. The conductive coil 41 includes a square coil or a rectangular coil, wherein the conductive coil 41 includes 3 turns, the width of the conductive coil is 20 mil, and the interval therebetween is 20 mil.
FIG. 2B is schematic view of another conventional planar embedded inductor device. The planar embedded inductor device comprises a substrate 50 and a magnetic layer 52 with high permeability (μr>1) disposed on the substrate 50. Note that the magnetic layer 52 is not patterned. A conductive coil 51 is disposed on the magnetic layer 52 with high permeability (μr>1). The conductive coil 51 electrically connects a conductive layer 56 on the back of the substrate 50 through a via hole 56 or contact plug, thereby generating a loop. The conductive coil 51 includes a circular coil, wherein the conductive coil 51 includes 3 turns, the width of the conductive coil is 20 mil, and the interval therebetween is 20 mil. Although the inductance (L) of the convention planar embedded inductor devices can increase using a magnetic layer 52 with high permeability (μr>1), however, the conventional method does not noticeably improve the quality factor.